Vapor phase corrosion inhibition



Patented Apr. 8, 1952 UNITD STATES TENT OFFICE VAPOR PHASE CORROSION INHIBITION Delaware No Drawing.- Application January 12, 1948, Serial No. 1,893

7 Claims. (Cl. 21-2.5)

Thepresentv invention relates to prevention of corrosion. of metal parts, which corrosion normally-occursin thepresenceof air (oxygen) and water; vapor and/or aqueous condensates-.. More particularly, this invention pertains to novel inethods'and compositions capable of inhibiting such: corrosion by providing an: atmosphere containing one or more of the present-novelvapor phase. inhibitors. In one of itsembodiments, this: invention. relates to packaging. of metals in such; a manner that corrosionthereof by moist air; prevented.

During, storage, handling, transportation, etc. ofiobjects. having corrodible metal or. metal-containing surfaces, more especially those of fer.- ruginous metals, suchv asvarious steels or fer rous: alloys, it is often desirable to prevent corrosion, of thesemetals. Heretofore, the various methods used for this purpose have been unsatisfactory becauseoi inadequate prevention of corrosion, cumbersomeness, and/or the-necessity of using anexcessive amount of labor and expenditure of time.

Partially or completely enclosed. metal parts are usually housed; packagedboxed, enveloped, or. placed in av container under such. conditions that. water vapor. and airare either. present, or are introduced tov the metal parts at the time of theirbeing disposed therein, or water. vapor with air enters through the enclosure walls after packaging;

Itis anobjectof this invention toobviateior materially reduce the-above defects of the prior art. It is an-objectto provide novel methods andmeans for inhibiting-corrosion of corrodible metals. It is. another object toprovide. certain compounds as corrosion-inhibitors". which will preventwater andaix (oxygen) from corroding metals, particularly. steel. A further object is to..introduce certainvolatile or vaporizable corrosion-inhibitors suitable. forpreventing watercorrosion of metals disposed in an enclosed space. A still. further object. is tO-PIOVlde .novel'means of. enclosing a. metal and inhibiting. moist" air corrosion of the. enclosed metall Another'ooj ect isto provide materials containing or impregnated with certain corrosion-inhibitors which latter volatilize therefrom and prevent moistair cor rosion of'metal'p'arts in thesubstantial'vicinity thereof; Still another object'is'to provide introduction of an atmosphere containing certain corrosion inhibitorvapors whereby metal parts intcontact with this atmosphere are significantly reducedand even prevented irom their otherwise normal aqueous'corrosion. V

Ithas'now been "discovered that the above-and other objects may be attained, and that particularly the'corrosion of the surfaces of a corrodible metal in the presence of water and oxygenmaybe prevented by contact of said surfaces with vapors of a compound having a nucleus ofthe general formula wherein X is a sulfur; selenium or oxygen atom or angroup and y is-an integer from 1' to 4-, inclusive; wherein the unsatisfied bonds- (as shown in above formula) are satisfiedbyhydrogenatoms and/or by organic radicals substantially non-corrosive or inert under theoperating conditions andso'long a's-the compoundhas a vapor pressureof-at least 0. 00002 mmtof Hg at 21 C. Particularly-useful organicsubstituents on said nucleus" are the conventionally known non-corrosive organic radicals, preferably hav ing up to about 20 carbon atoms. Within this general class of organic" substituents, especially desirable are the commonly known non-corrosive hydrocarbon and/or oxyhydrocarbon organic radic'als-;- Said single" valencebondsmay thus be satisfied by the hydrogen atom, as"well as by alkyl, alkenyl, cycloalliyharalkyl, aralkenyl, ar-yl, alkaryl, alka-ry-lalkyl,- hete'ro'cyclic,- or" terp'enic radicals, and any two or more of these single valence bonds may be joined together via an organic cycle to form a "second ring which may bealicjyclic, heterocyclic', terpenic, or aromatic attached to'the specified nucleus. The single valence bonds may be. satisfied by carbalkoxy, acyloxy, particularly carbethoxy; acetyl etc. groups, and also by halog'en-atoms; particularly chlorine orbromineatOms. Othersubstantially neutral substituents or: at least non-corrosive substituent groups may-:b'e present; this excludes corrosivesubstituents such as sulfonici acid; free mercapt'an" groups, and otherrkn'own corrosively active substituents. I'iiiallicases for the present purposes; there must-be present at least one nitro group attached to the: above hetero'cyclic ring nucleus whicli is oi the. class of nitrothiophenes; nitrofurans; nitrose'lenophenesand nitr'opyrrolesi It is'desirable; in order? to obtain fast corrosion-inhibiting: action and practically complete protection,i. to: have: the organic sub-' stituentsionsaid nucleus) have a: total of up to about ten carbon: atoms, which substituents may be alkyl, cycloalkyliaryl,- and/or phenyl radicals. Preferredi substituentsi are these described hydrocarbon radicals? In general, most i we).

is referred to herein under the term of nitroheterophene nucleus and compounds containing this nucleus are termed here1n "nitroheterophene compounds.

Suitable examples of the above described hydrocarbon radical substituents on the specified nitro-heterophene nucleus, are:

Alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, amyl, octyl, dodecyl, and tneir homologues;

Alkenyl groups such as allyl, methallyl, crotyl, octenyl, oleyl, etc.;

Cycloaliphatic or naphthenic such as cyclohexyl, alkylated cyclohexyl, methylcyclopentyl, cyclopentyl, cyclohexenyl, -etc.;

Aralkyl such as benzyl, alkylated benzyl, phenylethylene, phenylalkylene radicals, etc.;

Aryl radicals such as phenyl group, a fused benzene ring, i. e. attached by two adjacent carbon atoms of the nitro-heterophene nucleus, a naphthalene ring similarly fused, etc.;

Heterocyclic radicals such as oxazine, morpholine, thiazoline, pyrazole, piperazine, pyrrolidine radicals, etc.;

Terpinyl radicals such as bornyl, fenchyl, etc.

The organic substituents forming part of the present nitroheterophene structure or which are attached thereto, may contain stable polar substituents and/or radicals, e. g. chloro, fiuoro, alkoxy-ether, cycloalkoxy-ether, phenoxyether, thio-ether, ketone, ester, cyanate, nitrile, or nitro groups.

Of the above class of nitro-heterophene vapor phase corrosion-inhibitors, those containing a nitro-thiophene nucleus have been found to be most effective, while compounds containing a nitro-furan nucleus and compounds containing a nitro-pyrrole nucleus are of somewhat lesser efiectiveness, at least in some cases.

Most preferred'within any of these sub-genera are compounds in which the heterophene nucleus has a nitro group on the carbon atom alpha to the hetero atom. Examples of this are in the simplest cases, 2-nitro-thiophene, 2-nitro-furan, 2'-nitro-pyrrole, and their lower alkylated and also benzo substituted homologues and analogues.

One or more of the nitro-groups may be attached to either of the two beta positions, that is, positions 3 and/or 4, or in postions2 and 5, or in all of the four available positions. More preferred are compounds having not more than two nitro groups on the heterophene ring.

Examples of suitable compounds having a nitro-thiophene nucleus and applicable to the practice of this invention include: 2-nitro-thiophene, 3-nitro-thiophene, 2,5-dinitro-thiophene, 3-nitro-4,5-benzothiophene, and the various nitro derivatives of the substituted thiophenes and penthiophenes described in Beilstein, particularly in volume XVII, first series, pages 35-47 and pages 59, 60 and 66, and same volume of second series, pages 21 and 22.

Examples of suitable compounds having a nitro-selenophene nucleus and applicable to the practice of this invention include: Z-nitroselenophene and nitro derivatives of substituted selenophenes such as those e. g. of Beilstein, volume XVII, first series, page 42.

Examples of suitable compounds having a nitro-furan nucleus and applicable to the practice of this invention include: Z-nitro-furan, 3- nitro -furan, 2,5-dinitro-furan, 2-nitro-benzofuran, and the various nitro derivatives of the substituted furans described in Beilstein, particularly in volume XVII, first series, pages 27-29, 36, 38-43, 46, 54, 59 and 66, and same volume of second series, page 21.

Examples of suitable compounds having a nitro-pyrrole nucleus and applicable in the practice of this invention include: 2-nitr0-pyrrole,

3-nitro-pyrrole, 2,3-dinitro-pyrrole, 2,5-dinitropyrrole, 3-nitro-2,4-dimethyl-pyrrole, 3,5-dicarbethoxy-4-methyl-2-nitro-pyrrole, 2,5-diethyl-3- carbethoxy 4 nitro pyrrole, 4-acety1-5-nitropyrrole, 2,4-dinitro-3,5-carbethoxy-pyrrole, 2- nitro-indole, and the various nitro derivatives of the hydrocarbon and other organo and atomic radical substituted pyrroles described for example in Beilstein, volume XX, first series, page 169 et. seq., and same volume, second series, page 41 et seq.

- Nitrc-pyrroles may be prepared by nitration of pyrroles having a carboxyl, carbalkoxy, acyl, or halogen-substituent group. Pyrrole itself is destroyed by nitric acid. Mono-nitropyrroles may be prepared by action of a mixture of ethyl nitrate and sodium on pyrrole where, in this case, the sodium salt of the nitropyrrole is treated with carbon dioxide and the free mono-nitropyrrole thus liberated. Further to the preparation of nitropyrroles suitable for this invention, nitro groups retain the capacity exhibited in the cases of thiophene and furan of displacing acetyl, formyl, or even sometimes methyl groups; thus by this means of preparation, 2,4-dimethyl-3- carbethoxy-5-nitropyrrole is formed by the action of concentrated nitric acid upon 2,4-dimethyl-3-carbethoxy-5-acetylpyrrole.

In general, preparations of nitro-thiophenes, nitro-furans, and nitro-pyrroles are well known to the art of organic preparations and are described in standard reference books on this subject.

In general, for the present vapor phase corrosion-prevention methods, the class of nitroheterophene compounds should have a vapor pressure in excess of approximately 0.00002 mm. Hg at 21 C. Better results are obtained with nitro-heterophene compounds having a vapor pressure greater than about 0.0001 mm. Hg at 21C. More rapid inhibition of aqueous corrosion is obtainable with nitro-heterophene compound having a vapor pressure greater than about 0.001 mm. Hg at 21 C.

Most preferably, vapor phase corrosion-inhibition with nitro-heterophene compounds is carried out in a medium or atmosphere which is nearly neutral, preferably between a pH of approximately 6 and a pH of about 8. However, practical prevention of corrosion of steel is obtainable under conditions of pH as low as about 3.

The proportion or amount of one or more of the class of nitro-heterophene compounds which is to be introduced into and/or maintained in the atmosphere contacting a metal to prevent corrosion thereof, may vary within wide limits. The amount required for different conditions varies depending upon a number of variables,

sweater such as severity of conditions, temperature, degree ofhumidity, the particular nitro-heterophene compound introduced, and the manner in which it is introduced. Usually the placing of a piece of solid material, e. g. a sheet of paper or of a fibrous or like absorbent material impregnated with or coated by a nitro-heterophene compound, in the proximity of a corrodible metal enclosed in a container, or a package, or the like, provides satisfactory corrosion-inhibition when between about 0.01 gram and about 5.0 grams, preferably between about 1.0 gram and about-2.0 grams of the inhibitor(s) is present per each square foot of the inner surface of the container. Particularly satisfactory results are secured whenthe inhibitor is present in such an amount as to allow between about 0.01 gm. and about gm. (for average-conditions about-0.2 to 4 gm.) thereof for each cubic foot or enclosed vapor space.

The nitro-heterophene vapor phase inhibitors can be applied either separately or in various mixtures of members of this class, or with other discovered classes of vapor phase cOrrosion-in-- hibitors. In certain cases it is advantageous to apply a mixture containing a nitro-heterophene compound with relatively high vapor pressure (preferablyabove about 0.001 mm. Hg at 21 C.) and another nitro-heterophene compound having a relatively low vapor pressure (e. g. between about 0.0005 and 0.00002 mm. Hg at 21 0.).

Compositions containing the present inhibitors are efiective in gaseous, liquid, or solid form so long as vapors of the inhibitor(s) may contact-;;

the metal to be protected from corrosion.

Various techniques are effective in the utilization of the present nitro-heterophene compounds as vapor phase corrosion-inhibitors. Within any enclosure means, corrosion of metal surfaces by moisture is prevented. by enclosing, or making available therein, one or more of the specified nitro-heterophene compounds. The latter can be originally introduced as a solid, 9. liquid, or a vapor, or in solution, as an emulsion or dispersion, etc., as long as the inhibitor may vaporize and thus be present in the atmosphere around the metal. the inhibitor(s) may be disposed in the enclosure as crystals or as a powder; or the metal article or the wrapping material thereof may be coated with material containing the inhibitor(s); orthere may be introduced into the enclosure or container a piece of solid, e. g. absorbent, preferably fibrous material, coated or impregnated with a nitro-heterophene compound. Thus, paper, cloth, various textile materials, ethylcellulose, any sheet or filamentous material, which is coated or impregnated with the inhibitor(s) may be inserted near or wrapped around the metal parts. In one of the preferred embodiments of the invention it is advantageous to use paper which is impregnated with a nitro-heterophenecompound. The metal parts may be enclosed within a covering or packaging material, only one side of which allows disposal of vapors of the contained inhibitor(s) to the contiguous atmosphere. Laminates of paper, parts of which are impregnated with or contain the inhibitor (5) are also useful. Asphalt papers may also be used as suitable carriers of the inhibitor(s). After providing the containers with the inhibitor(s) in any of the above, or like modes, these containers may then be closed or sealed. The resultantcone tainer or package does not have to be completely In the case of enclosed metal articles,"

closed orimpervious to vapors orgases, butonly by partially or-substantially saturating the in troduced air with vapors of the inhibitor(s). Metal-parts can be effectively corrosion-proofed lay-coating them with the inhibitor(s) by depositing thelatter from a solution or a dispersion thereof, or from heated vapors contacting a metal,

or-by-incorporating the inhibitor(s) in relativelynon-volatile coating materials which remain on the metal.

The metal walls or parts enclosed within tanks,

pipes, machinery, or instruments are prevented from corroding by either enclosing or making the inhibitor(s) available within the vapor spaces present therein. This is also true in hydrauli callyoperated mechanisms. In a preferred method the inhibitor(s) is disposed in and. allowed to vaporize from a hydraulic fluid introduced into such mechanisms. When disposed in a liquid, the nitro-heterophene compounds not only inhibit corrosion of metals contacting this liquid but also inhibit corrosion of metals contacting the vapor phaseabove the liquid.

Aerosols are also effective for distributing the inhibitor(s). In such-a case, the in-hibitoris dis-- solved in a liquefied, normally gaseous solvent which is under sufiicient pressure in a vessel tov maintain the solvent in its liquid state. The solution of the inhibitor thus prepared is released through an orifice .in the vessel, thereby distributing the inhibitor in a state of minutesubdi vision.

The present inhibitors areeflective agentsforreducing corrosive wear of moving machined metalv parts, particularly in engines,.e. g. steam engines, steam turbines, internal combustion engines, etc. The inhibitors are incorporated into fueling or lubricating media for such engines or for other metal parts in machinery, such as organiclubricants and thereby the wear attendant upon corrosion is inhibited.

Stability of the'present class of nitro-hetero phene compounds, particularly at elevated temperatures above room temperature, is-improved, and undesirable decomposition of the nitroheterophene compounds which may'sometimes occur is even practically entirely eliminated by the simultaneous presence of a basic-acting agent. The latter may be defined as an alkaline agent and/or a compound which reacts as a base in the presence of acidic-reacting materials. Preferably, it is advisableto employ organic or inorganic compounds which, when dispersed in water, yieldan aqueous'phase or tend to maintain a dispersion or solution having a pH value of at least approximately 6. As such stabilizers, minor'amounts (with respect to the nitroheterophene compound) of amines, cyclic-nitrogen and heterocyclic organic bases, guanidine, amine carbonates, amine bicarbonates, alkali and alkaline earth metal bicarbonates and carbonates and similarly basic'materials may be employed with advantage. In general, strong alkali and alkaline earth metal hydroxides are to be avoided althou h they may be usedin some cases depending upon circumstances which are readily determinable by a small-scale empirical or pilot test. The amount of a basic-reacting stabilizer should usually be between about 0.1% and about 25% by weight of the nitro-heterophene compound(s) depending upon the acidity of the conditions encountered, although larger or smaller amounts may be used. A few specific stabilizers which are here mentioned are: dicyclohexylamine bicarbonate, also this amines carbonate and sodium bicarbonate. For purposes of further illustration, reference will now be made to the following examples, it being understood that there is no intention of being limited to the specific details therein.

Samples of steel strips of low carbon content, A1 inch by 2 inches, with thoroughly cleaned surfaces were dried and weighed. The steel strips were then suspended in the upper part of closed glass containers, into which various amounts of the compound to be tested, as set forth in the table below, were disposed. Distilled water was also. placed separately within each of the glass containers. The steel pieces under test were not in contact with any of the unvaporized form of the compounds being tested for corrosion-inhibition. After the duration of each test, the weight changes of the steel strip samples were measured.

Weclaim as our invention: 1 H I p I 1. In a method for inhibiting corrosion of a ferruginous metal occurring by contact with water vapor and air, the step of providing, in the proximity of a ferruginous metal, a vaporous atmosphere containing a corrosion-inhibiting amount of 2 -nitro-thiophene.

2.111 a method for inhibiting corrosion of a ferruginous metal occurring by contact with water vapor and. air, the step of providing, in the proximit of a ferruginous metal, a vaporous at-. mosphere containing a corrosion inhibiting amount of 3-nitro-thiophene.

3. A method for inhibiting corrosion of a fer- 15 ruginous metal surface by contact with water vapor and air comprising placing said metal surface and 2,5-di-nitro-thiophene in a condensed state in locations relative to each other such that the metal surface is contacted by a corrosiong inhibiting concentration of vapors given on by the condensed 2,5-di-nitro-thiophene.

4. The combination of a ferruginous metal object normally corrodible by contact with water vapor and air, an atmosphere containing a corg rosion-inhibiting amount of 2-nitro-thiophene,

and a container enclosing said atmosphere and metal object.

5. In a method for inhibiting corrosion of a fer- Visually Parts by 9 E 23 Observed Inhibi or Weigh Time Temp-1 of Steel 0! In- Days F. Mini; Against hlbitor rams Rusting g (Approx) Per Cent None None 7 150 102. 2 Z-Nitrothiophene. 0. 5 7 150' O. 9 9D o-Nitrotoluene O. 5 7 150 61. 4 l5 o-Nitro-iso-propyl-benzene. 0. 5 7 150 34. 2 l p-Nitro-iso-propyl-benzene 0. 5 7 150 39. 6 l0 2-Nitrothiophene 0. 5 7 150 1. 2 85 Z-Nitrothiophenc. 0. l 14 150 0. 7 90 Z-Nitrothiophcne. OJ 1 28 100 0. 5 95 2-Nitrothiophe11e 0. 6 1-1 100 0. 2 95 2-Nitro-p-cymene 0. 1 7 150 89. l oNitrodiethyl-aniline. 0. 1 7 150 57. 1 5 o-Nitrodiphenyl-ether. 0. 1 7 150 29. 4 p- Iitrofiuoro-benzene. 0. l 7 150 52. 7 l5 2-Nitro-3-methoxy-tolucne 0. 1 7 150* 125. 7 0

1 Completely covered with rust. 5 Covered with black rust scales.

It will be noted from the data in the above table that a wide variety of nitro-aromatic nuclei not containing the nitro-heterophene nucleus (two double bonds in a five-membered ring conjugate with the hetero atom therein) were tested under comparative conditions and found to give weight increases due to rusting varying from approximately 30 to 125 times that found from the use of a compound containing a nitro-heterophene nucleus. In view of the above tests, the presence of a nitro group in an aromatic compound or even in a hetero-atomic aromatic compound is not sufiicient' to significantly inhibit rusting, On the other hand, the results from em ployment of a nitro-heterophene compound show practically negligible weight increases due to rusting, and the steel was substantially protected by the vapors of such a compound. The above significant differences in corrosion-inhibition were not due to differences in volatility or lack of vaporization since the non heterophene compounds are of comparable volatility to nitroheterophene compounds which give good protection under similar conditions.

ruginous metal object by contact' with water vapor in air, the steps comprising enclosing said metal in a container containing a corrosion-inhibiting amount of 2-nitro-thiophene.

6. In a method for inhibiting corrosion of a ferruginous metal occurring by contact with watervapor and air, the step of providing in the proximity of a ferruginous metal, a vaporous' atmosphere containing a corrosion-inhibiting amount of an unsubstituted nitro-thiophene containing from one to two nitro groups, said nitrothiophene having a vapor pressure of at least 0.001 mm. "rig at 21 C,

7. In a method for inhibiting corrosion of a ferruginous metal occurring by contact with water vapor and air, the step of providing, in the proximity of a ferruginous metal, a vaporous atmosphere containing a corrosion-inhibiting amount of a nitro-substituted thiophene containing from one to two nitro groups in substitution for'thiophene-hydrogen atoms, and in which the only other substituents are hydrocarbon radicals ranging in total carbon content from one to ten carbon atoms, said nitro-thiophene having a vapor pressure of at least 0.0002 mm. Hg at The following references are of record in the ROBERT J. MOORE. AARON WACHTER.

REFERENCES CITED Number Name Date Kern Feb. 28, 1939 Number 10 Name Date Shoemaker May 30, 1939 Lamprey Sept. 19, 1939 Beekhuis Nov. 5, 1940 Downing Jan. 5, 1943 Wachter et a1 Apr. 22, 1947 Walb Oct. 19, 1948 Brooks et a1. Sept. 6, 1949 

1. IN A METHOD FOR INHIBITING CORROSION OF A FERRUGINOUS METAL OCCURRING BY CONTACT WITH WATER VAPOR AND AIR, THE STEP OF PROVIDING, IN THE PROXIMITY OF A FERRUGINOUS METAL, A VAPOROUS ATMOSPHERE CONTAINING A CORROSION-INHIBITING AMOUNT OF 2-NITRO-THIOPHENE. 